Field Of The Invention
The present invention relates to an improved expanded foamed bead of a rubber-modified styrene polymer. More particularly, the present invention is concerned with an expanded foamed bead of a rubber-modified styrene polymer, comprising a plurality of closed cells defined by cell walls which constitute a matrix for the bead. Each of the cell walls comprises two surfaces separated by a distance equal to the thickness of the cell wall. The matrix comprises: (a) a continuous styrene polymer phase; and (b) a rubber phase dispersed in said continuous styrene polymer phase (a), wherein the rubber phase comprises a plurality of substantially flat, butadiene polymer rubber particles each having at least one styrene polymer particle occluded therein; wherein the flat rubber particles are arranged in a specific lamellar configuration along the thickness of the cell wall. The expanded foamed bead of a rubber-modified styrene polymer of the present invention is excellent in its ability to retain a foaming agent gas within the closed cells, and can advantageously be employed for producing, for example, packaging materials and cushioning materials or packings which are improved in resistance to breakage, such as cracking.